Grinding wheel dresser



Oct. 6, 1959 M, QSPLACK 2,907,314-

GRINDING WHEEL DRESSER Filed Sept. 22, 1955 14 Sheets-Sheet 1 INVENTOR J J05 Z Y I PLAC- ATTORNEY Oct. 6, 1959 J. J. osPLAcK GRINDING WHEEL DRESSER Filed Sept. 22, 1955 14 Sheets-Sheet 2 (R007 LINE MM 4 a R007 LINE) bREssM/c STROKE (DRIVE 5/05 INVENTOR I J05 PHJ 0 PurK BYZ I 7 1 a ATTOR EYS DRESS/NC STROKE (COAST SIDE) Oct. 6, 1959 J. J. OSPLACK GRINDING WHEEL DRESSER l4 Sheets-Sheet 3 Filed Sept. 22, 1955 LINE OF ACTION 0F DIAMOND CU T R INVENTOR Jos PHJ, OSPLACK BY jm M M X 1% ATTORNE 0a. 6, 1959 J. J. OSPLACK 2,907,314

GRINDING WHEEL DRESSER Filed Sept. 22, 1955 14 Sheets-Sheet 4 J lNVEyOR o EPH .Osmaa BYjM ah/aw ALWW a J ATTORNE Oct. 6, 1959 .1. J. OSPLACK GRINDING WHEEL DRESSER Filed Sept. 22, 1955 14 Sheets-Shee t 5 INVENTOR Josspu J. 05pm I M w ATTORNE s Oct. 6, 1959 J. J. OSPLACK 2,907,314

v GRINDING WHEEL DRESSER Filed Sept. 22, 1955 14 Sheets-Sheet 6 LINEOF ACTION (COAST SIDE) N m INVENTOR $27M J, OSPLACK BY M ATTOR EYS Oct. 6, 1959 J. J. OSPLACK 2,907,314

GRINDING WHEEL DRESSER Filed Sept. 22, 1955 14 Sheets-Sheet 7 COAST SIDE DR! VE SIDE INVENTOR JOEZPH J, OSPLACK BY W ATTORN V Oct. 6, 1959 J, J, OSPLACK 2,907,314

GRINDING WHEEL DRESSER File d Sept. 22, 1955 14 Sheets-Sheet a "Hull" DRIVE 5105\. 306' COAST SIDE INVENTOR ATTORNE 5 Oct. 6, 1959 OSPLACK 2,907,31-1

GRINDING WHEEL DRESSER Filed Sept. 22, 1955 l4 Sheets-Sheet 9 INVENTOR Jo EPH J; OSP'LACK BY Z4 M ATTORNE 5 WA, W/ej Oct. 6, 1959 J. J. OSPLACK GRINDING WHEEL DRESSER l4 Sheets-Sheet 10 Filed Sept. 22, 1955 m T N E V m \{ZsEPI-I J, OSPLACA ATTORNEYS Oct. 6, 1959 J. J. OSPLACK 2,907,314

GRINDING WHEEL. DRESSER Filed Sept. 22, 1955 14 Sheets-Sheet 11 LINE OFACT/ N COAST s/os INVE'NTOR JOSEPH J, OSPLACK BY h .92, 44% M 2 1 ATTORN Y5 Oct. 6, 1959 J. J. OSPLACK GRINDING WHEEL DRESSER l4 Sheets-Sheet 12 Filed Spt. 22, 1955 m T N E V m J, OSPLACK M, W 7 W X ATTORNEYS JOSEPH BY Q Oct. 6, 1959 J. QSPLACK 2,907,314

GRINDING WHEEL DRESSER Filed Sept. 22, 1955 14 Sheets-Sheet 13 .INVENTOR J0 J,O PlACK BY ZffL mla ATTO NEYS Oct. 6, 1959 J. J. OS PLACK 2,

GRINDING WHEEL DRESSER Filed Sept. 22. 1955 14 Sheets-Sheet 14 MOD/ /ED TRUE INVOLUTE TOOTH FORM MODIFIED 7 00777 FORM TRUE FORM OF TOOTH 0N WHEEL MODIFIED 700 TH FORM START OF MOD/F/ED TOOTH FORM, VENTOR F R 5Q UVALENT 0 PM Jo EPHJ, Ospuc ON TOO TH BY W ATTOR E United Patent GRINDING WHEEL DRESSER Joseph J. Osplack, Detroit, Micln, assignor to Vinco'Corporation, Detroit, Mich, a corporation of Michigan Application September 22, 1955, Serial No. 535,931

'5 Claims. (Cl. 125-11) dressed and to the contacting surfaces of two mating gear teeth, which surfaces represent the direction of pressure between two mating gear teeth or between a gear tooth and a grinding wheel thread. For involute gears, the line of action represents the path of the contact point as the gears rotate.

When a gear is ground by the hobbing process, the contact point between the grinding thread and the gear tooth moves along the line of action as the wheel and work piece rotate. In grinding a true involute gear, the line is straight. 0n the wheel itself, the contact point follows a spiral path on the thread curving in toward the root on one face of the thread and outward from the root on the other face. If a diamond or cutting element in contact with the Wheel thread is moved along the line of action as the wheel rotates, it dresses the same spiral path of the wheel that is used in grinding a gear. Therefore, in one pass along a line of action, the diamond dresses a surface that will generate a perfect involute on a gear provided the line-of-action is straight.

A particular grinding spiral comes into use only when the work piece is located in a particularangular position under the wheel. in any other position, a different contact are dressed in a series of dressing strokes which run parallel to the axis of the wheel. Such a method of dressing the wheel takes an undue amount of time and does not produce the required accuracy of thread as is required in the manufacture of quality gears. This is particularly true when the gears are to be ground by the hobbing process from a solid blank such as disclosed in my Patent No. 2,607,175, granted August 19, 1952, and entitled Method of Making Precision Gears. In the grinding of gears as disclosed in that patent, the rack teeth of the wheel move as the wheel rotates in mesh with the work I teeth of the gear to be ground, advancing one circular pitch with each revolution of the grinding wheel. The wheel generates the complete tooth contour as each tooth rotates in mesh with the threads. The wheel starts a cut on one tooth while completing a cut on another, and the threads of the grinding wheel progress from tooth to tooth in a smooth, continuous grinding action. For most of the time that the tooth is in mesh with the threads, it is being ground on both sides simultaneously by the thread that proceeds it and the thread that follows it.

In using the generally accepted method of dressing a threaded grinding wheel, that is, by dressing the wheel on a lathe, any ridges and hollows on the flanks of the teeth of the wheel due to irregularities of the dressing diamond or movement of the dressing diamond along the flank of the tooth produces a pattern of ridges and hollows which follow a series of concentric circles. Such concentric circles produce errors in the flanks of the teeth of the gear to be ground by the wheel and produce unnecessary roughness of these flanks. It is, therefore, an object of this invention to provide for a novel method for dressing the flanks of a threaded grinding wheel which may be completed in a short time and produce an accurate, smooth surface which will follow a predetermined contour.

It is a further object of this invention to provide for a device by which both flanks of a threaded grinding wheel may be dressed at the same time in order that the process of truing the same may be shortened.

It is still a further object of my invention to provide means whereby the path of thedressing diamond over the flank of a thread of the grinding wheel may be modified in order that the gear to be ground may itself have a modified form.

Broadly, I propose to pass the dressing diamond along the line of action of the rack form of the threaded grinding wheel and the gear which is to be formed by it. Such a line is normal to the flank of the thread being spiral would generate the finished contour on the work piece. Therefore, to be able to grind in any angular position of the wheel, it is necessary to dress the complete flank surface of the wheel threads. This is accomplished by shifting the diamond over and dressing along a different line of action, and repeating this process until the faces of the threads have been completely dressed. Both faces of the thread are dressed at the same time, and the wheel is rotated at high speed so that the dressing action is very fast and is completed in a short time.

In comparing the line-of-action dresser with conventional dressing methods, the significant difference lies in the period of time required to dress a complete contact spiral. Diamond wear becomes a factor if it is great enough to cause an appreciable dilference in thread contour between the beginning and end of a grinding spiral. Since a line-of-action dresser finishes a complete contact spiral with each pass, diamond wear aifects accuracy only by tile negligible amount it wears during one .pass along the line of action. v

If the wheel is dressed by a conventional dresser with repeated passes parallel to the axis of the wheel, the diamond will have made many passes through the wheel between the time it dresses the beginning and the end of any grinding spiral. The diamond thus travels a much greater distance and requires a much longer time cycle to produce an effective grinding spiral surface, and any diamond wear occurring during this extended cycle will be reflected in the tooth profile,

If a diamond breaks during conventional dressing, it is necessary to redress the complete wheel since it does not have even one fully-dressed contact spiral. If a diamond breaks during line of action dressing, all contact spirals dressed up to that point are satisfactory for grinding and do not have to be redressed.

Since diamond wear and breakage are not as critical with a line of action dresser, the wheel can operate at high speed for fast dressing, and the dresser can take cuts that are deep enough to finish the wheel in one series of passes.

In a conventional dressing usually a series of light cuts are taken over the complete surface of the thread faces, and then these light cuts are repeated one or more times until the wheel surface has been dressed to the required contour and depth. This procedure not only requires much more time, but the final series of very light finishing cuts leaves a glazed surface on the wheel so that it does not cut as cleanly, tends to load'up with metal more quickly, and therefore, cannot be used to remove I Y 3 stock from the workpiece at a fast rate. The single series of full-depth cuts made with the line of action dresser leaves the wheel surface free-cutting so that it can grind gears fast and accurately, usually in a single pass, Without loading the wheel with metal particles too quickly. Modification of the thread profile to produce a special tooth shape is accomplished simply and easily with a line of action dresser and does not add to the dressing time. A modification cam in the dresser varies the dresser action so that a special thread profile is produced automatically as the wheel is dressed. In conventional dressing usually at least one added series of dressing passesis required to modify the thread profile.

.My line of action dresser comprises generally, a cutting element mounted in a feed slide which in turn is carried in a main slide which is movable parallel to the line of action in the dressing stroke and in synchronization with the rotation of the grindingwheel so that the main slide will move a distance equal to the circular pitch for each complete rotation of the grinding wheel. Means are provided for retracting the feed slide into the main slide, returning the main slide to the start of a new dressing stroke and then bringing the cutting element into engagement with the grinding wheel so that it will dress along a difierent line of action parallel to the first line of action. Further means are provided for controlling the root diameter or the depth of cut into the grinding wheel near either of the two ends of the dressing stroke. In order that the threaded grinding wheel may produce gears of modified design, means are provided whereby the travel of the dressing contour may be varied from a straight line. Further means are included in the de ice so that the dressing diamond or cutting element may be accelerated during movement in particular directions in order that the overall dressing process may be shortened.

The broad application of having a dressing diamond move along a line of action in order to dress a threaded grinding wheel is in itself not new. Rickenmann, 2,177,583, discloses broadly the theory of line of action dressing although the precise term line of action is not used in the patent. Applicant's device differs from Rickenmanns device in that the main slide supporting the feed slide and cutting element is movable parallel to the line of action, while Rickenmanns main slide moves parallel to the axis of the threaded grinding wheel. Rickenmann does not disclose any means for accelerating the return movement of the slide nor does he disclose any means for modifying the direction of the line of action to produce a modified thread form.

Referring to the drawings in which a preferred embodiment of my invention is disclosed and in which prime numerals denote like parts:

Fig. 1 illustrates the path of contact between a rack form of a threaded grinding Wheel which is in bobbing engagement with a gear;

Fig. 2 is a schematic view showing a dressing diamond following a line of action of a threaded grinding Wheel;

Fig. 3 is a schematic end view of Fig. 2 showing the spiral path resulting from engagement of the dressing diamond with the threaded grinding wheel;

Fig. 4 is a schematic perspective view of Fig. 3 showmg a different view of the spiral path;

Fig. 5 is a schematic view showing the respective dressmg strokes of a cutting tool on the drive side of a threaded grinding wheel;

Fig. 6 is a schematic view of the respective dressing strokes on the coast side of the threaded grinding wheel of Fig. 5;

Fig. 7 is a schematic view of means for controlling depth of cut on the drive side;

Fig. 8 is a schematic view showing means for controlling depth of cut on the coast side;

Fig. 9 is a perspective view showing a gear grinder adapted to receive a dresser of my novel design;

Fig. 10 is an enlarged perspective view of the mount of the gear grinder shown in Fig. 9 for receiving my novel dresser;

Fig. 11 is a schematic perspective view showing a gear train connected to the spindle drive for driving the dresser unit of my invention and the headstock of the grinder of Fig. 9; a

Fig. 12 is a perspective view of a line of action dresser unit constructed according to my invention;

Fig. 13 is a broken front view of the dresser unit of Fig. 12 illustrating the detail of the ratchet mechanism for altering the feed of the dressing diamond;

Fig. 14 is a broken rear view of the dresser of Fig. 12 as viewed along line 1414;

Fig. 15 is a rear sectional view of the dresser of Fig. 12 showing the position of the various elements in the middle of a dressing stroke;

Fig. 16 is similar to Fig. 15. except that the dressing diamonds are shown at the end of a dressing stroke;

Fig. 17 is a view looking from rear to from showing detail of the return stroke accelerating mechanism at the beginning of a return stroke;

Fig. 18 is a similar view to Fig. 17 showing theposition of the return stroke mechanism at the beginning of a dressing stroke;

Fig. 19 is a plan view of Fig. 14 taken along line 1919;

Fig. 20 is a sectional view of Fig. 15 taken along line 20--20;

Fig. 21 is a detailed view of a tooth of a gear to be ground showing a true involute tooth as compared with a modified tooth;

Fig. 22 is a detailed view showing the true involute form of a threaded grinding wheel tooth as compared with a modified tooth form for grinding the tooth of Fig. 21; and

Fig. 23 is a detailed view of the modified tooth mecha nism of the dresser of Fig. 12.

Referring to Fig. 1 in order to visualize the theoretical workings of my novel dresser, 1 represents a threaded grinding wheel rotating in a direction as shown and 2 denotes a gear which is in mesh with the rack form of the grinding wheel. If the threaded grinding wheel 1 rotates in hobbing engagement with the gear 2, then the gear will turn one circular pitch for each complete rotation of the grinding wheel. If the flanks of the threads of the grinding wheel are straight, the successive points of contact between the gear and the grinding wheel will follow a straight line and these points will generate on the gear itself true involute teeth. For convenience sake, I call the side of the gear tooth whose front flank rotates up into mesh with the wheel threads the drive side of the gear and the flank of the tooth of the gear which approaches the following thread near the inner diameter of the thread, the coast side of the gear. The side of the wheel thread whose front flank first rotates into mesh with the gear is called the drive side of the wheel while the flank of the wheel thread which approaches the following tooth of the gear is called the coast side of the wheel. The lines of action for the drive and coast sides of the threaded grinding wheel 1 are labeled A--A and B-B, respectively.

Fig. 2 shows a cutting element 3 mounted in a main slide 4 which is movable on a guide 5 wherein the guide 5 lies parallel to the line of action AA. If the guide 4 is moved in synchronization with the rotation of the wheel, then the pointof contact between the cutting element and wheel will produce a uniform spiral 6 on the wheel as shown in Fig. 3 which starts at the tip 7 of a thread and continues until it contacts the root diameter at point 8. This motion through space is shown perspectively in Fig. 4 where it is seen that a perfect spiral is produced. Of course, the movement of the slide with respect. tp the rQlfiDn of the threaded wheel must equal pivoted arm 17 a minute amount exactly one circular pitch for each rotation of the threaded grinding wheel in order to produce the uniform spiral.

.moves in a dressing stroke 20, then moves in a retrac- 'tion stroke 21 in order to clear the threads, moves in a return stroke 22 to its original starting point and then is brought into engagement again with the flank 10 of the first thread of the wheel 1 in an engagement stroke 23. Upon each complete cycle of the cutting element, it must move an increment X normal to the original dressing stroke in order that the complete flank of the thread may be dressed.

Fig. 6 illustrates the motion of the cutting element on the coast side of the threaded grinding wheel. For convenience, the elements on the coast side of my dresser are referred to with primenumerals, the numerals being the same for similar elements and motions as on the drive side of the dresser. The motion of the dressing element on the coast side is directly opposite to that of the dressing element on the drive side so that the cutting element 3 initially starts at the root diameter of the threaded grinding wheel instead of at a tip of a thread as on the drive side.

It is seen by referring to Figs. 5 and 6 that if the cutting element is to dress the complete width of a wheel having a number of threads, that there will have to be means for limiting the depth of cut into a wheel as the cutting element approaches the root diameter. Such a means for limiting the depth of cut is illustrated schematically in Figs. 7 and 8. The cutting element 3 is spring-biased by spring 11 so that it is forced out of the main slide 4.

machine modified to receive my dresser. The grinder denoted generally by the numeral 100 comprises a spindle 101 having mounted thereon a threaded grinding wheel 102. The grinder has the conventional headstock drive mechanism 103 mounted on table 104.

Referring to Fig. 10 there is shown an adaptor 150 having an upper portion 151 and a lower portion 152. Lower portion 152 is movable longitudinally of the table 104 while upper portion 151 is rotatably mounted on the lower portion 152. The drive for the adaptor is taken off the main spindle 101 by means of shafts 152 and 153 operating through gear boxes 154 and 155 which turn a spline 156 along which the adaptor is slidable. Mounted on upper portion 151 is a bracket 157 upon which the dresser unit may be mounted. The dresser unit receives its driving power through shaft 158 and cams 160 and 160 carried in the adaptor.

Reference is now made to Fig. 11 which illustrates a drive for the particular adaptor shown. The'drive from spline 156 is taken off through gears 159, 160 and 161 to turn the spline 162 which in turn provides power to the adaptor. Mounted on the end of spline 162 is a bevel gear 163, which in turn is in engagement with a second bevel gear 164. Bevel gear 164 is mounted on shaft 165 The cutting element 3 has projecting from it an arm 12 i which is adapted to engage a root template 13 which will force the cutting element 3 down into the slide against the bias of spring 11. As .is seen in Fig. 7, thearm 12 when initially at the start of the dressing stroke is out of contact with the root template. As the cutting element approaches and contacts the root diameter as shown by the dotted lines, the arm will then contact the root template so that any further movement of the slide 4 along the line of action will depress the cutting element into the slide thus limiting the depth of cut into the wheel 1.

The rate or amount of feed of the cutting element 3 normal to the line of action is controlled by a ratchet 14 which is adapted to be engaged at the end of each return stroke by a prong 15. Mounted on the ratchet 14 is a cam 16 which is so proportioned that it will move the for each engagement of the ratchet 14 with the prong 15. It is thus seen as the ratchet rotates in the direction shown, that it will force the arm 17 to pivot about its pivot point and feed the cutting element in a minute direction normal to the line of action and parallel to the flank of the thread being dressed for each complete dressing cycle of the slide. It is obvious that the finer the teeth of the ratchet, that smoother will be the flank of the threads being dressed.

Fig. 8 illustrates the drive for controlling the feed of the cutting element for the coast side of the dresser.

The principle of operation is the same as that shown in Fig. 7 except that here the cutting element and arm 17 move in an opposite direction from that in Fig. 7. That is, the feed of the cutting element is directed out of the slide 4' a minute amount upon each complete cycle of the slide 4'.

Now that the general principles of my invention have been disclosed, reference is now made to the remaining drawings which illustrate a working model of my invention. Fig. 9 is a perspective view of a bobbing grinding Whose axis of rotation is the axis about which the upper portion 151 may rotate. Shaft in turn provides power to turn shaft 166 through means of bevel gears 167 and 168. Mounted on the end of shaft 166 is a spur gear 169 which drives a second spur gear 170 through means of a speed-changing gear 171. Gear 170 in turn provides power to worm 171 which turns gear 172. Gear 172 in turn is mounted on shaft 158 which provides the drive power for the dressing unit.

Reference is now made to Fig. 12 which illustrates perspectively a dressing unit constructed according to my invention denoted generally by the numeral 200 which is mounted on the upper portion 151 of the adaptor. The dressing unit 200 comprises generally a base portion 201 which is slidably mounted on the bracket 157 of the upper portion of the adaptor. The base portion 201 has movably mounted upon it main slides 300 and 300' which are slidable in guides 202 and 202'. Guides 202 and 202' extend parallel to the line of action and may be made in any adjustable form by means of sine bars, etc. Slides 300 and 300 roll upon ball bearings 203' which are carried in a groove in the guide 202' as shown in Fig. 14. Mounted on guides 300 and 300' are cam followers 301 and 301' which have rollers 302 and 302 on their ends. These rollers are adapted to follow cams 160 and 160' which are mounted onshaft 158. The cams are so shaped that cam 160 will pull slide 300 upon its dressing stroke along the guide 202, while earn 160 pushes slide 300' down the guide 202' on its dressing stroke. A spring (not shown) is positioned between the slide and the base portion 201 to bias the cam roller 302' into firm contact with the cam 160'. The force of gravity acting on slide 300 serves to provide sufficient engagement between the cam roller 302 and the cam 160.

Referring to Fig. 13 there is illustrated the detailed working of the ratchet mechanism for controlling the rate of feed of the cutting diamonds 305 and 305' into the threaded wheel. Cutting diamonds 305 and 305 are mounted on arms 306 and 306. The arms in turn are mounted on feed slide blocks 307 and 307" which are adapted to slide vertically in pivoted blocks 308 and 308' as shown in Fig. 14'. The blocks ride upon ball bearings 309 which in turn run in grooves carried inthe pivoted blocks. The feed slide blocks are continually pulled in an upward direction by means of tension springs 310 and 310'which are connected to a projecting arm which in turn is mounted on the pivoted block. Pivot arms 311 311' are adapted to rotate about pivot points 312 and 312' to bear against the top of feed slide blocks through shaft as ratchets 316 and 316.

tensionof the springs. The pivot arms 311 and 311 in turn are actuated by means for cams 313 and 313 which are mounted coaxially with spur gears 314 and 314'. Spur gears 314 and 314 in turn are rotated by second spur' gears 315 and 315 which are mounted on the same Ratchets 316 and 316' are adapted to be engaged by prongs 317 and 317' when the main slides have reached the end of their return stroke and are in position for the start of the dressing stroke.

As seen in Fig. 13, when ratchet 316 contacts prong 317, it will be rotated in the counterclockwise direction. This in turn will cause spur gear 314 and cam 313 to rotate in clockwise direction. The drop of cam 313 will m turn allow the pivot arm 311 to rotate clockwise about pivot point 312 due to the tension of spring 310 acting on feed slide block 307. As the main slide completes a dressing cycle, the ratchet 316 will be actuated one -notch so that eventually the complete surface of the flanks of the threads of the grinding Wheel will be dressed. By making the teeth of the ratchet finer, or by changing the ratio of spur gears 315 and 314, the amount of feed may be changed correspondingly to either provide a coarse feed or a smooth feed. Brakes 318 and 318' serve to prevent movement of ratchet 316 when it is not in contact With the prong 317.

The retraction of the cutting diamonds 305 and 305 from the threaded grinding wheel so that they may clear the grinding wheel upon their return stroke is achieved by arms 400 and 400 pushing the feed slide block down against the tension of springs 310 and 310. This is done when the main slide reaches an end of its dressing stroke. The pivoted arms 400 and 400' are caused to rotate about pivot points 401 and 401' carried on the main slides when actuated by push bars 402 and 402'. Push bar 402, as seen in Fig. 13, in turn is moved by a cam follower 403 which is pivoted about point 404. Cam

follower 403 has mounted on it a roller 405 which rolls upon the cam surface of cam 406. Cam 406 in turn is mounted coaxially with a spur gear 203 which is driven .through means of a speed changing gear 204 by spur gear 205. Spur gear 205 is driven by spur gear 206 which is mounted coaxially with the shaft 158 carried in. the adaptor 150. The cam surface of cam 406 may be varied in order to provide proper acceleration and deceleration of the feed block in order that the complete unit may be operated at a high speed.

The depth of cut is regulated by means of root templates 500 and 500' as shown in Figs. and 12. These templates contact rollers 501 and 501 which are mounted on the feed slide blocks. As the rollers contact templates 500 and 500' they will cause the feed slide blocks to be forced down into the pivot blocks and so regulate the depth of cut and root diameter of the grinding wheel.

' Reference is now made to Figs. 15, 16, 17 and 18 in order to explain the working of the accelerating mechanism which is used to accelerate the return stroke 'of the main slide. Gear 203 is mounted coaxially on the same shaft with an arm 600 which in turn has mounted on its end a roller 601. Roller 601 is adapted to engage an accelerating arm 602 at the beginning of the dressing stroke to cause a rapid advance of the main slide. The purpose of this is to prevent undue stress between the cam 160 and cam roller 302 during the initial stroke since part of the strain of moving the main slide will be absorbed by the roller 601 contacting the arm 602. It is seen by referring to Fig. 17, that as the arm 600 continues to rotate about its shaft in the direction shown, that the roller 601 will engage a slot 603 which is carried in a skirt connected to the main slide. The roller will initially engage the slot at the beginning of the return stroke and continue to engage the slot during the complete'retum stroke. Since the roller 601 rotates about a point, its greatest lateral speed with respect to the movement of diamond 305 will be when it is vertical to the line of movement of diamond 305 and slide 300. At that position the roller will be at the bottom of slot 603 so that the slide will be traveling at its greatest speed at this point. The arm 601 will, therefore, accelerate the slide from zero at the start of the return stroke to a certain speed when the roller rests at the bottom of the slot. From this point the slide will decelerate to zero at the end of the return stroke.

It is sometimes desirable to manufacture a gear having a modified tooth form from that of a true involute. This is especially true wh'en the gears are manufactured to be operated under a'relatively heavy load so that the possibility of tooth deflection must betaken into consideration. If the gears rotate only in one direction, it may be that the modified form of the tooth flank will only be required on one side, while the other side is left a true involute. Again, under certain design conditions it may be desired to have a tooth of greatly modified form which does not even approach the involute form. In order to illustrate how my invention may be used to modify grinding wheels used in grinding modified gears, reference is now made to Figs. 21, 22 and 23.

Fig. 21 illustrates a tooth 700 of a gear having flanks of true involute form. The dotted lines 701 indicate a flank of a gear having a modified involute form. Fig. 22 denotes an enlarged cross section of a thread 702 of a grinding wheel used in grinding true involute teeth such as represented by tooth 700. A grinding wheel which is modified to produce the modified tooth form 701 of Fig. 21 is shown by dotted lines 703'. Fig. 23 shows the device for modifying the thread of the grinding wheel as shown in Fig. 22. The modification of the thread is accomplished by making the pivot block 308 movable about a pivot point 704. Pivot point 704 is integral with the main slide 300 and has also mounted on it a pivot arm 705. Pivot arm 705 has mounted at one end a roller 706 which is adapted to ride upon a cam surface which is carried on the base portion 201. The cam surface may have modifying cams 707 and 708 attached to it so that as the roller 706 passes over them, they will cause the arm 705 to move and so move the pivot block 308. A tension spring 709 continually biases the roller 706 in contact with the cam surface and also against a set screw 710.

In order to completely understand the operation of the device, a complete cycle of one of the dressing diamonds will be followed through, it being understood that the cycle of the other dressing diamond is similar in operation. The dressing diamonds are brought into initial contact with the threaded grinding wheel and the dressing unit started. It is not necessary that the diamonds be in any particular angular position with the grinding wheel but only that they be initially placed along a line of action. As the machine is turned on, the cam will rotate in a clockwise direction as seen in Fig. 12 pulling the main slide 300 up the guide 202. Since this guide is parallel to the line of action, it necessarily follows that the dressing diamond 305 will follow a line parallel to the line of action. As the dressing diamond approaches the root diameter of the threaded grinding wheel, the roller 501 which is mounted on the feed slide block will contact root template 500, thus as the main slide continues to travel up the guide, the feed slide block will be forced downwardly against the tension of spring 310.

As the main slide reaches the end of its dressing stroke the rise of cam 406 will contact the roller 405 pushing the arm 403 in an upward direction. This in turn will move push bar 402 and so move arm 400 about pivot point 401. Arm 400 will force the feed slide block to retract downwardly and move the diamond 311 to rotate in a counterclockwise direction as seen in Fig. 13 to allow the feed slide 307 to rise a minute amount so that the diamond 3&5 is in position to dress a new line of action which is parallel to but slightly displaced from the original line of action.

As the main slide starts on its new dressing stroke, the roller 601 will be in contact with the accelerating arm 602 so relieving a part of the load carried by cam followers 3fi6 and cam 160. The dressing unit will then complete similar cycles until the complete threaded gear has been dressed. 1

While I have shown my dressing unit as being mounted on a grinder and being driven by power being taken from the spindle, it is obvious that the dress- 1 ing unit could be driven directly from the headstock or the tailstock. It is also obvious that the dressing .unit alone could comprise a separate machine having its own power source which then could be used to dress many grinding wheels. The only requirement Would be in such a dresser that the rotation of the spindle carrying the threaded grinding wheel be synchronized with the movement of the dressing diamonds.

I claim:

1. In apparatus for dressing a rotating threaded grindingwheel used in grinding a gear, the improvement comprising a dresser having a slide, a cutting element movably mounted in said slide, a guide rail having a starting point and a stopping point in which said slide is movably mounted, said guide rail extending parallel to a line of successive points of pressure between said gear and a flank of a thread of said wheel when said wheel is in grinding engagement with said gear, means for moving said slide in said guide rail in a first dressing stroke from said starting point to said stopping point in synchronization with the rotation of said wheel, means for retracting said cutting element in said slide away from said wheel, means for returning said slide to its starting point while said cutting element is in a retracted position, and means for bringing said cutting element into dressing contact with said wheel in position for a second dressing stroke,

10 said second dressing stroke being laterally displaced and parallel to said first dressing stroke.

2. A dresser according to claim 1 having in addition means for accelerating the movement of the return stroke of said slide'with respect to the movement of said dressing stroke.

3. A dresser according to claim 1 having a first cam means for modifying the position of said cutting element with respect to said slide as said slide moves in said guide rail on its dressing stroke from its starting point to its stopping point to eifectively modify the contour of the flank of the thread being dressed.

4. A dresser according to claim 1 having in addition a second cam means for controlling the root diameter of said threaded wheel, said second cam means retracting said cuttin element in said slide at one end of said dressing stroke as said cutting element contacts said threaded wheel at its root diameter.

5. A method of dressing a threaded grinding wheel used in grinding a gear by moving a cutting element in a series of cycles; each cycle comprising moving said cutting element in dressing engagement with said grinding wheel in a dressing stroke along a line of action between a rack form of said grinding wheel and a tooth of said gear and in synchronization with the rotation of said grinding wheel; moving said cutting element parallel to the axis of rotation of said grinding wheel when said cutting element approaches the root diameter of said grinding Wheel at the end of a dressing stroke; withdrawing said cutting elernent in a withdrawal stroke in a direction normal to said line of action when said cutting element reaches an end of said wheel; returning said cutting element in a return stroke parallel to said line of action after the cutting element has cleared the threads of said wheel at the end of said withdrawal stroke; and engaging said cutting element with said grinding wheel in an engagement stroke in a direction normal to said line of action when said cutting element reaches a point opposite the start of said dressing stroke, said engagement stroke moving said cutting element a different distance on each completecycle of said cutting element.

References Cited in the file of this patent UNITED STATES PATENTS 2,177,583 Rickenmann Oct. 24, 1939 2,188,016 Schicht Jan. 23, 1940 2,434,810 Osplack Jan. 30, 1948 2,619,950 Rickenmann Oct. 2, 1952 

